Semiconductor manufacturing method

ABSTRACT

This invention provides a method for manufacturing a semiconductor using a wafer carrier: the temperature of a wafer can be uniformed and the uniformity within the surface excels with few differences of the composition distribution; a crystal is grown by forming a plurality of grooves to uniform the temperature of the wafer surface by diffusing heat, at the bottom of a wafer pocket to mount a wafer on a wafer carrier inside a crystal growth apparatus chamber; and the groove depth is deeper at the peripheral part of the wafer than at the central part thereof while the groove density is higher at the peripheral part of the wafer than at the central part thereof. The following examples are the groove pattern; a groove with a plurality of wedge-shaped grooves formed widening from the central part toward the peripheral part, a groove with a plurality of circular grooves formed narrowing the interval thereof from the central part toward the peripheral part, a groove filled with circular grooves with the diameter shortened from the central part toward the peripheral part, and a groove filled with square grooves with the side shortened from the central part toward the peripheral part. All the grooves deepen toward the peripheral part.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturing a semiconductor by using a crystal growth apparatus in which a crystal growth is carried out by decomposing a source gas thermally on a wafer heated to reach a high temperature, especially by using a vertical MOVPE (Metal Organic Vapor Phase Epitaxy) apparatus of high speed revolution type.

[0003] 2. Description of the Related Art

[0004] In the crystal growth using the MOVPE apparatus, the following document is disclosed as a method for improving an uniformity within a surface of a wafer of a growth layer: document “2001, International Conference on Indium Phosphide and Related Materials Post Deadline Papers pp.15-16. 13th IPRM 14-18, May 2001 Nara, Japan”.

[0005] Recently, since an epitaxial wafer, a wafer with a thin film layer grown, is used in most of an electronic device, a mass production technology of the epitaxial wafer is indispensable. VPE (Vapor Phase Epitaxy), MBE (Molecular Beam Epitaxy), MOVPE and so on are currently in practical use as an epitaxial growth technology.

[0006] In the epitaxial growth technology, the MOVPE to be described in the present invention is a method for growing a thin film crystal of chemical compound semiconductor on a wafer by reacting III-group organic metal with V-group gas on the heated wafer. In order to mass-produce by using this MOVPE, a multi-charge method to grow a plurality of crystals at the same time is indispensable, and one of the method in practical use currently is the method of vertical and high speed revolution type. In this method of vertical and high speed revolution type, since the crystal is grown uniformly inside the wafer surface by charging the wafer with the surface thereof up and by flowing a reaction gas vertically, that is, in a longitudinal direction, a susceptor holding wafer is revolving.

[0007] In the crystal growth, however, the temperature distribution of the surface of the wafer in which the crystal is actually grown becomes different according to the way of thermal conduction of a wafer holder. And then, the following problems occur: the efficiency of a source gas decomposition on the surface of the wafer changes; the composition also changes sensitively; and the uniformity within the surface deteriorates due to the difference of composition distribution within the surface.

[0008] In the document mentioned above, using the change of band gap wavelength with the change of composition due to the temperature, and relating to a method for controlling wave length in the crystal growth using the MOVPE apparatus, there is disclosed a method for improving the uniformity by controlling the wavelength within the surface after improving controllability by controlling directly the change of temperature owing to the type of gas introduced and the change of flow rate.

[0009] In order to examine the temperature distribution within the surface of the wafer, a PL (Photo Luminescence) peak wavelength is actually measured when a four element mixed crystal of indium gallium arsenic phosphorous (InGaAsP) with the band gap wavelength of 1.3 micrometers is grown by the MOVPE apparatus. The PL is to measure an impurity level contained in the crystal by observing a light emitted from a semiconductor, changing the wavelength of light radiated to the semiconductor. In this case, a band gap wavelength distribution within the surface of the wafer can be obtained.

[0010] In this band gap wavelength distribution, that is, the composition distribution, the wavelength is long at the central part and shifts to be short as nearing the peripheral part of the wafer with the shape of concentric circle or almost the same shape. There can be recognized that the temperature distribution within the wafer surface becomes higher by approximately 3-4° C. as shifting from the central part to the peripheral part of the wafer, by inversely converting the wavelength distribution from the dependence on growth temperature of the band gap wavelength.

SUMMARY OF THE INVENTION

[0011] The present invention has been achieved in view of aforementioned problems. The object of the present invention is to provide a novel and improved method for manufacturing a semiconductor in which the temperature of the surface of the wafer can be uniformed and which excels in the uniformity within the surface with few differences of the composition distribution.

[0012] In the aspect of the present invention to achieve the above object, there is provided a method for manufacturing a semiconductor wherein a crystal growth is carried out by using a jig for crystal growth with a plurality of grooves formed to uniform the temperature of the surface of the wafer by diffusing heat, at the part to mount a wafer on a wafer carrier inside a crystal growth apparatus chamber, at the bottom of a spot facing part, for example. Preferably, the depth of the plurality of grooves is deeper at the peripheral part of the wafer than at the central part of the wafer. Also preferably, the density of the plurality of grooves is higher at the peripheral part of the wafer than at the central part of the wafer.

[0013] In addition, the crystal growth may be carried out not by forming the grooves directly at the bottom of the spot facing part but by forming a plurality of grooves formed to uniform the temperature of the surface of the wafer by diffusing heat, at a spacer plate placed on the spot facing part as an underlay of the wafer.

[0014] Further, the crystal growth may be carried out by forming directly a plurality of grooves formed to uniform the temperature at the rear surface of the wafer to be mounted or by forming a plurality of grooves at an insulating film formed at the rear surface of the wafer.

[0015] There are following examples of pattern of groove to uniform the temperature of the surface of the wafer: as the first example, a groove with a plurality of wedge-shaped grooves formed widening from the central part toward the peripheral part and deepening toward the peripheral part at the same time; as the second example, a groove with a plurality of circular grooves formed narrowing the interval thereof from the central part toward the peripheral part and deepening toward the peripheral part at the same time; as the third example, a groove filled with circular grooves with the diameter shortened from the central part toward the peripheral part and deepening toward the peripheral part at the same time; and as the fourth example, a groove filled with square grooves with the side shortened from the central part toward the peripheral part and deepening toward the peripheral part at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other features of the invention and the concomitant advantages will be better understood and appreciated by persons skilled in the field to which the invention pertains in view of the following description given in conjunction with the accompanying drawings which illustrate preferred embodiments.

[0017]FIG. 1A is a schematic perspective view inside a chamber of a MOVPE apparatus concerning the first-fourth embodiments and FIG. 1B is a sectional view on the line A-A of a MOVPE apparatus concerning the first-fourth embodiments.

[0018]FIG. 2 is an explanatory diagram showing the pattern of groove of wafer pocket, spacer plate, the rear surface of wafer or insulating film concerning the first-fourth embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the preferred embodiment of the present invention will be described in reference to the accompanying drawings. Same reference numerals are attached to components having same functions in following description and the accompanying drawings, and a description thereof is omitted.

[0020] (First Embodiment)

[0021] With regard to the first embodiment, a schematic perspective view inside a chamber of a vertical MOVPE crystal growth apparatus of high speed revolution type is illustrated as FIG. 1A. FIG. 1B is a sectional view showing typically on the line A-A of a MOVPE apparatus shown as FIG. 1A. Preferably, a material for a wafer carrier 10 to set a wafer is easy to be processed, capable of achieving a good thermal conduction and hard to be corroded with a material gas, such as carbon graphite and molybdenum. The wafer carrier 10, a jig for crystal growth, is placed on a susceptor 30 and heated on a heater 40 under the susceptor 30. The susceptor 30 supported by a rotation shaft 50 revolves so that the crystal growth may be uniform within the wafer carrier.

[0022] On the wafer carrier 10, a plurality of spot facing parts (hereinafter, referred to as a wafer pocket 20) to set the wafer horizontally are formed. Although FIG. 1 is illustrated so that three wafers can be grown at the same time, the same goes for any number of wafers. In the vertical MOVPE apparatus, a source gas flows in from the upper part of wafer inside the chamber to react on the heated wafer and the crystal grows. For example, when growing a four element mixed crystal of InGaAsP, such an organic metal as trimethyl indium and triethyl gallium is used as the material of In and Ga belonging to III-group element while arsine and phosphine are used as the material of As and P belonging to V-group element. And the crystal growth is carried out on the wafer by decomposing these elements thermally.

[0023] As explained in the description of the related art, the band gap wavelength distribution of a growth layer, that is, the composition distribution thereof, shows that the wavelength is long at the central part and shifts to be short as nearing the peripheral part of the wafer with the shape of concentric circle or almost the same shape. It is judged that the temperature distribution within the wafer becomes higher by approximately 3-4° C. as shifting from the central part to the peripheral part of the wafer, by converting from the dependence on growth temperature of the band gap wavelength and from the result of the wavelength distribution.

[0024] The reason for high temperature of the peripheral part of the wafer is as follows. Although thermal conduction is good at the part of the wafer pocket 20 owing to its thin part, heat is conducted from the rear surface of the wafer set at the wafer pocket 20 to the surface thereof and becomes hard to be conducted to the surface. The reason for this is that the heat conductivity of the wafer is lower than that of the wafer carrier 10, and the temperature distribution shows that the temperature becomes lower as shifting toward the central part of the wafer.

[0025] Consequently in this embodiment, assuming in advance that the thermal conduction is growing lowered as shifting toward the central part of the wafer, the thermal conduction is varied to uniform the temperature within the surface of the wafer by processing a plurality of grooves to diffuse heat at the peripheral part of the wafer, at the bottom of the wafer pocket 20 so that the temperature distribution within the wafer may become uniform.

[0026] Examples of pattern diagram are illustrated as FIGS. 2A-D a groove is carved at the bottom of the wafer pocket. The explanation is as follows with regard to the pattern of each groove and the structure thereof. In any patterns, the depth of the plurality of grooves formed is deeper at the peripheral part of the wafer than at the central part of the wafer while the density of the plurality of grooves formed is higher at the peripheral part of the wafer than at the central part of the wafer. Further, the grooves must be optimized according to the crystal growth apparatus and to growth condition. If filling this condition, the process inside the pocket is not limited to the examples of groove patterns shown in FIGS. 2A-D, of course.

[0027] As an example of groove pattern, a pattern shown in FIG. 2A can be applied with a plurality of wedge-shaped grooves formed along the periphery circle, widening from the central part (circumference of a circle with approximately half the diameter of the periphery circle, for example) of the wafer pocket toward the peripheral part and deepening toward the peripheral part at the same time.

[0028] As an example of groove pattern, a pattern shown in FIG. 2B can be applied with a plurality of circular grooves formed narrowing the interval thereof from the central part (circumference of a circle with approximately half the diameter of the periphery circle, for example) of the wafer pocket toward the peripheral part and deepening toward the peripheral part at the same time.

[0029] As an example of groove pattern, a pattern shown in FIG. 2C can be applied with a groove filled with circular grooves with the diameter shortened from the central part (a circle located at the center of the periphery circle, with approximately one-third of the diameter of the periphery circle, for example) of the wafer pocket toward the peripheral part and deepening toward the peripheral part at the same time.

[0030] As an example of groove patterns, a pattern shown in FIG. 2D can be applied with a groove filled with square grooves with the side shortened from the central part (a square located at the center of the periphery circle, having a side with the length of approximately one-third of the diameter of the periphery circle, for example) of the wafer pocket toward the peripheral part and deepening toward the peripheral part at the same time.

[0031] By setting the wafer at the wafer pocket having grooves processed as described above in the MOVPE, the crystal growth is carried out. The method for crystal growth and the kind of growth film are to be designed according to an apparatus to be used and an object of using. Also, the growth condition needs to be designed in accordance with the process of the wafer pocket.

[0032] As the difference of temperature distribution of the surface of the wafer is reduced and the uniformity of thermal decomposition of the source gas on the surface thereof is improved, owing to a grooving process inside the pocket, the crystal composition also becomes capable of growing uniformly. At this time, since the thermal decomposition of V-group source gas is empirically changed due to the change of temperature distribution, the composition distribution changes due to the change of take-in factor. However, since it is known that the take-in factor of III-group source gas for deciding a growth thickness does not change so much, the distribution of thickness does not change.

[0033] (Second Embodiment)

[0034] In the second embodiment, a groove is formed on a spacer plate placed on the wafer pocket without making the grooving process directly on the wafer pocket as in the first embodiment. Mounting the spacer plate with the grooving process made, on the wafer pocket, on which the wafer is set. Preferably, a material for the spacer plate is high purity carbon and molybdenum, or a semiconductor wafer such as indium phosphaide (InP), gallium arsenide (GaAs) and silicon (Si).

[0035] FIGS. 2A-D can be applied as a pattern diagram of groove on the spacer plate at this time. A plurality of grooves are formed on the spacer plate without making the grooving process on the wafer pocket. The depth of the plurality of grooves is deeper at the peripheral part of the spacer plate than at the central part thereof while the density of the plurality of grooves is higher at the peripheral part of the spacer plate than at the central part thereof. With regard to the groove patterns, a detailed explanation is to be omitted since it is the same as in the first embodiment.

[0036] In this embodiment as in the first embodiment, as the difference of temperature distribution of the surface of the wafer is reduced and the uniformity of thermal decomposition of the source gas on the surface thereof is improved, the crystal composition also becomes capable of growing uniformly. In the first embodiment, however, since a product is subject to accumulate on the groove formed on the wafer pocket due to the gas flowing into the rear surface of the wafer in the crystal growth process, it becomes necessary to replace or clean the wafer carrier. On the contrary in this embodiment, since it is sufficient to replace or clean the spacer plate, the versatility improves.

[0037] By mounting the spacer plate with the grooving process made, on a normal wafer pocket, and by setting the wafer on the spacer plate, the crystal growth is carried out in the vertical MOVPE apparatus of high speed revolution type. The method for crystal growth and the kind of growth film are to be designed according to an object of using. As for the growth condition, it is necessary to consider the growth temperature, the gas flow rate and the like since the crystal grows on the wafer on the spacer plate.

[0038] (Third Embodiment)

[0039] In the first and second embodiments, a process is made on a jig in the MOVPE apparatus. In this third embodiment, on the other hand, a groove is formed directly on the rear surface of the wafer in order to uniform the thermal conduction. The same pattern as the one shown in FIGS. 2A-D can be applied as the processing pattern of groove at this time. In the case of an element manufactured by using a normal crystal growth wafer, since a rear polishing is carried out in the final step of manufacturing the wafer to make the wafer thin-film, the element is not affected as a chip even if forming the groove on the rear surface.

[0040] A groove is formed having the pattern to uniform the thermal conduction, on the rear surface of the wafer before the crystal starts growing, by using a photolithography step and an etching step that are used generally in processing a surface of wafer conventionally. Patterning the groove by a photoresist by using a mask for patterning and the like, and carrying out wet or dry etching, a plurality of grooves are formed. The depth of the plurality of grooves is deeper at the peripheral part of the wafer than at the central part thereof while the density of the plurality of grooves is higher at the peripheral part of the wafer than at the central part thereof. With regard to the groove pattern, a detailed explanation is to be omitted since it is the same as in the first and second embodiments.

[0041] In this embodiment, it is unnecessary to process the wafer carrier to uniform the temperature distribution and to prepare the spacer plate. Since a pattern groove is formed directly on the wafer, a heat distribution does not change as growing due to the product accumulating on the groove during the crystal growth, to improve the reproducibility of crystal growth. In addition, since the rear groove disappears in the end during the rear polishing process, the assembly process and the characteristics are not affected.

[0042] After forming the groove on the rear surface of the wafer as described above, and then setting the wafer at a normal wafer carrier pocket, the crystal growth is carried out in the vertical MOVPE apparatus of high speed revolution type under the growth condition considering the rear groove. The method for crystal growth and the kind of growth film are to be designed according to an object of using.

[0043] (Fourth Embodiment)

[0044] In this fourth embodiment, by forming an insulating film on the rear surface of the wafer and forming the same groove as in the third embodiment on the insulating film in order to uniform the thermal conduction, the difference of composition distribution is reduced. The groove pattern at this time is also the same as shown in FIGS. 2A-D. In addition, the rear insulating film can be easily etched after the crystal growth.

[0045] An insulating film such as a silicon oxide film is formed on the rear surface of the wafer before the crystal starts growing, by using a CVD method. After that, a groove is formed having the pattern to uniform the thermal conduction, on the insulating film by using a photolithography step and an etching step. Patterning the groove by a photoresist by using a mask for patterning and the like, and carrying out wet or dry etching, a plurality of grooves are formed on the insulating film. The depth of the plurality of grooves is deeper at the peripheral part of the wafer than at the central part thereof while the density of the plurality of grooves is higher at the peripheral part of the wafer than at the central part thereof. With regard to the groove pattern, a detailed explanation is to be omitted since the same groove is formed on the rear surface of the wafer as in the first, second and third embodiments.

[0046] Also in this embodiment, it is unnecessary to process the wafer carrier and to prepare the spacer plate to be processed as in the third embodiment. Since a pattern groove is formed directly on the insulating film formed on the rear surface of the wafer, a heat distribution does not change as growing due to the product accumulating on the groove during the crystal growth, to improve the reproducibility of crystal growth. In addition, since the pattern groove on the rear surface can be easily removed together with the insulating film after the crystal has grown, other wafer processes are not affected.

[0047] After forming the insulating film on the rear surface of the wafer as described above, and then setting the wafer grooved in order to uniform the thermal conduction, at a normal wafer carrier pocket, the crystal growth is carried out in the vertical MOVPE apparatus of high speed revolution type under the growth condition considering the rear insulating film. The method for crystal growth and the kind of growth film are to be designed according to an object of using.

[0048] Although the preferred embodiment of the present invention has been described referring to the accompanying drawings, the present invention is not restricted to such examples. It is evident to those skilled in the art that the present invention may be modified or changed within a technical philosophy thereof and it is understood that naturally these belong to the technical philosophy of the present invention.

[0049] Although in the embodiments the crystal growth is carried out by using a vertical MOVPE apparatus of high speed revolution type, the present invention can be applied to the case that the crystal growth is carried out by using a horizontal MOVPE apparatus of wafer rotation type into which a source gas flows in a direction horizontal to the wafer.

[0050] According to the present invention as described above, to cope with the problem that the composition distribution fails to be uniform due to the difference of temperature of the central part within the wafer surface from the peripheral part thereof in the crystal growth in the MOVPE apparatus, the thermal conduction distribution in the crystal growth becomes uniform and a crystal with a uniform composition distribution within the wafer surface can be grown by forming a plurality of grooves with a low density and a shallow depth at the central part, on the wafer pocket in the apparatus or by preparing the spacer plate to be placed between the wafer carrier and the wafer, to form a plurality of grooves with the same pattern as the wafer carrier mentioned above, on the spacer plate.

[0051] Also, the thermal conduction distribution in the crystal growth becomes uniform and a crystal with a uniform composition distribution within the wafer surface can be grown by providing a step of forming a plurality of grooves with a low density and a shallow depth at the central part, on the rear surface of the wafer before the crystal starts growing or by forming the insulating film on the rear surface of the wafer, to provide a step of forming a plurality of grooves similar to the ones mentioned above, on the insulating film. 

What is claimed is:
 1. A method for manufacturing a semiconductor wherein a crystal growth is carried out by using a wafer carrier with a spot facing part formed to mount a wafer comprising the step of: carrying out the crystal growth by mounting a wafer at the bottom of the spot facing part with a plurality of grooves formed to uniform the temperature of the surface of the wafer by diffusing heat.
 2. A method for manufacturing a semiconductor according to claim 1 wherein the depth of the plurality of grooves formed at the spot facing part is deeper at the peripheral part of the wafer than at the central part of the wafer.
 3. A method for manufacturing a semiconductor according to claim 1 wherein the density of the plurality of grooves formed at the spot facing part is higher at the peripheral part of the wafer than at the central part of the wafer.
 4. A method for manufacturing a semiconductor wherein a crystal growth is carried out by using a wafer carrier with a spot facing part formed to mount a wafer comprising the step of: carrying out the crystal growth by mounting a wafer on a spacer plate placed on the spot facing part and with a plurality of grooves formed to uniform the temperature of the surface of the wafer by diffusing heat.
 5. A method for manufacturing a semiconductor according to claim 4 wherein the depth of the plurality of grooves formed at the spacer plate is deeper at the peripheral part of the wafer than at the central part of the wafer.
 6. A method for manufacturing a semiconductor according to claim 4 wherein the density of the plurality of grooves formed at the spacer plate is higher at the peripheral part of the wafer than at the central part of the wafer.
 7. A method for manufacturing a semiconductor wherein a crystal growth is carried out by using a wafer carrier with a spot facing part formed to mount a wafer comprising the steps of: forming a plurality of grooves to uniform the temperature of the surface of the wafer by diffusing heat, at the rear surface of the wafer; and carrying out the crystal growth by mounting the wafer with the plurality of grooves formed, on the spot facing part.
 8. A method for manufacturing a semiconductor according to claim 7 wherein the depth of the plurality of grooves formed at the rear surface of the wafer is deeper at the peripheral part of the wafer than at the central part of the wafer.
 9. A method for manufacturing a semiconductor according to claim 7 wherein the density of the plurality of grooves formed at the rear surface of the wafer is higher at the peripheral part of the wafer than at the central part of the wafer.
 10. A method for manufacturing a semiconductor according to claim 7 wherein the plurality of grooves are formed by using a photolithography step.
 11. A method for manufacturing a semiconductor according to claim 7 wherein the plurality of grooves are formed by using an etching step.
 12. A method for manufacturing a semiconductor according to claim 7 wherein the plurality of grooves are removed by carrying out a rear polishing after the crystal growth.
 13. A method for manufacturing a semiconductor wherein a crystal growth is carried out by using a wafer carrier with a spot facing part formed to mount a wafer comprising the steps of: forming an insulating film on the rear surface of the wafer; forming a plurality of grooves to uniform the temperature of the surface of the wafer by diffusing heat, at the insulating film; and carrying out the crystal growth by mounting the wafer with the plurality of grooves formed, on the spot facing part.
 14. A method for manufacturing a semiconductor according to claim 13 wherein the depth of the plurality of grooves formed at the rear surface of the wafer is deeper at the peripheral part of the wafer than at the central part of the wafer.
 15. A method for manufacturing a semiconductor according to claim 13 wherein the density of the plurality of grooves formed at the rear surface of the wafer is higher at the peripheral part of the wafer than at the central part of the wafer.
 16. A method for manufacturing a semiconductor according to claim 13 wherein the plurality of grooves are formed by using a photolithography step.
 17. A method for manufacturing a semiconductor according to claim 13 wherein the plurality of grooves are formed by using an etching step.
 18. A method for manufacturing a semiconductor according to claim 13 wherein the insulating film with the plurality of grooves formed is removed by etching after the crystal growth.
 19. A method for manufacturing a semiconductor according to claim 13 wherein the insulating film is a silicon oxide film. 